[client] Reinject captured first packet on lazy connection activation (#6572)

client/iface/wgproxy/proxy.go

@@ -18,4 +18,9 @@ type Proxy interface {
 	RedirectAs(endpoint *net.UDPAddr)
 	CloseConn() error
 	SetDisconnectListener(disconnected func())
+
+	// InjectPacket writes a raw packet directly to the remote peer over the underlying transport,
+	// bypassing WireGuard. Used to replay the captured lazyconn handshake initiation. Only the
+	// kernel-mode proxies act on it; the userspace proxy is a no-op since reinjection is kernel-only.
+	InjectPacket(b []byte) error
 }